Re: [rtcweb] My Opinion: Why I think a negotiating protocol is a Good Thing

Neil Stratford <neils@belltower.co.uk> Tue, 18 October 2011 12:20 UTC

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Date: Tue, 18 Oct 2011 13:20:04 +0100
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From: Neil Stratford <neils@belltower.co.uk>
To: Harald Alvestrand <harald@alvestrand.no>
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Subject: Re: [rtcweb] My Opinion: Why I think a negotiating protocol is a Good Thing
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On Tue, Oct 18, 2011 at 12:43 PM, Harald Alvestrand <harald@alvestrand.no>wrote:

> I believe we need to standardize a negotiation protocol as part of RTCWEB.
> This needs to be described as a protocol, and cannot usefully be described
> as an API.
>

I strongly disagree. We need an API, not a protocol. This is a fundamentally
different problem to traditional RTC due to the presence of the javascript
execution engine that can implement the protocol.


> A design criterion for RTCWEB has been that it should be possible to write
> applications on top of RTCWEB simply - that is, without deep knowledge about
> the world of codecs, RTP sessions and the like.
>

Which can be achieved even with a low-level javascript API by leveraging
library code. We do not need to embed every bit of intelligence into the
browser to enable that to happen.


> Another design criterion is that interworking should be possible - which
> means that SOMEWHERE in the system, deep knowledge about the world of
> codecs, RTP sessions and the like must be embedded; we can’t just simplify
> our options until everything’s simple.
>
> There’s one place in the ecosystem where this knowledge HAS to be - and
> that is within the browser, the component that takes care of implementing
> the codecs, the RTP sessions and the related features. If we can avoid
> requiring embedding it twice, that’s a feature.
>

Agreed - the browser handles RTP and codecs, and the javascript should
handle negotiation and protocol state machines.


> It used to be that I was a believer in APIs - that we should make the API
> the “king”, and describe the way you generate an RTP session as “you turn
> this knob, and get this effect”.
> After looking at the problem of Web applications that don’t have domain
> knowledge for a while, I’ve concluded that this doesn’t work. There’s the
> need for one browser to communicate with the other browser, and if the
> intermediate components are to have the ability to ignore the details,
> what’s communicated has to be treated like a blob - something passed out of
> one browser’s API and into another browser’s API, unchanged by the
> application - because the application must be able to ignore the details.
>

The application can equally ignore what a library does if it wants to, but
it's not tied to one library, it can pick the one most suited to the task in
hand.


> What’s more - we DO want to enable applications that are NOT simple.
> Including gateways, which are not browsers. So applications must be free to
> look inside the blob - break the blob boundary - when they need to. So this
> pulls in the same direction as the need for interoperability - the format,
> semantics and handling rules for these blobs has to be specified. In some
> detail.
>

This is the problem with passing blobs through an API. If we had a low-level
API we wouldn't be passing blobs.

Neil